Redis is an advanced key-value store which is pretty simple to install and use. Using multiple redis instances, you can have master-slave replication without breaking any sweat. Bringing it somewhat further, you can use redis sentinels to monitor your master and have a nifty failover system for high-availability.
Compiling redis
# install required packages yum install gcc make tcl # download redis tarball curl -O http://download.redis.io/releases/redis-2.8.6.tar.gz # extract tarball tar xvzf redis-2.8.6.tar.gz # change directory to extracted directory cd redis-2.8.6 # compile redis make # execute tests (requires tcl) make test
Starting with one master redis server
# redis_01.conf daemonize yes pidfile /var/run/redis_6379.pid port 6379 tcp-backlog 511 timeout 0 tcp-keepalive 0 loglevel notice logfile "./redis_6379.log" databases 16 save 900 1 save 300 10 save 60 10000 stop-writes-on-bgsave-error yes rdbcompression yes rdbchecksum yes dbfilename dump_6379.rdb dir ./ slave-serve-stale-data yes slave-read-only yes repl-disable-tcp-nodelay no slave-priority 100 appendonly no appendfilename "appendonly.aof" appendfsync everysec no-appendfsync-on-rewrite no auto-aof-rewrite-percentage 100 auto-aof-rewrite-min-size 64mb lua-time-limit 5000 slowlog-log-slower-than 10000 slowlog-max-len 128 notify-keyspace-events "" hash-max-ziplist-entries 512 hash-max-ziplist-value 64 list-max-ziplist-entries 512 list-max-ziplist-value 64 set-max-intset-entries 512 zset-max-ziplist-entries 128 zset-max-ziplist-value 64 activerehashing yes client-output-buffer-limit normal 0 0 0 client-output-buffer-limit slave 256mb 64mb 60 client-output-buffer-limit pubsub 32mb 8mb 60 hz 10 aof-rewrite-incremental-fsync yes # start first redis-server src/redis-server redis_01.conf
Adding a slave redis server
# redis_02.conf daemonize yes pidfile /var/run/redis_6380.pid port 6380 tcp-backlog 511 timeout 0 tcp-keepalive 0 loglevel notice logfile "./redis_6380.log" databases 16 stop-writes-on-bgsave-error yes rdbcompression yes rdbchecksum yes dbfilename dump_6380.rdb dir ./ slaveof 127.0.0.1 6379 slave-serve-stale-data yes slave-read-only yes repl-disable-tcp-nodelay no slave-priority 100 appendonly no appendfilename "appendonly.aof" appendfsync everysec no-appendfsync-on-rewrite no auto-aof-rewrite-percentage 100 auto-aof-rewrite-min-size 64mb lua-time-limit 5000 slowlog-log-slower-than 10000 slowlog-max-len 128 notify-keyspace-events "" hash-max-ziplist-entries 512 hash-max-ziplist-value 64 list-max-ziplist-entries 512 list-max-ziplist-value 64 set-max-intset-entries 512 zset-max-ziplist-entries 128 zset-max-ziplist-value 64 activerehashing yes client-output-buffer-limit normal 0 0 0 client-output-buffer-limit slave 256mb 64mb 60 client-output-buffer-limit pubsub 32mb 8mb 60 hz 10 aof-rewrite-incremental-fsync yes # start second redis-server src/redis-server redis_02.conf
Starting up first sentinel to monitor the redis master
# sentinel_01.conf port 26379 daemonize yes logfile ./sentinel_26379.log sentinel monitor mymaster 127.0.0.1 6379 2 sentinel down-after-milliseconds mymaster 30000 sentinel parallel-syncs mymaster 1 sentinel failover-timeout mymaster 180000 # start first sentinel src/redis-sentinel sentinel_01.conf
Adding another sentinel
# sentinel_02.conf port 26380 daemonize yes logfile ./sentinel_26380.log sentinel monitor mymaster 127.0.0.1 6379 2 sentinel down-after-milliseconds mymaster 30000 sentinel parallel-syncs mymaster 1 sentinel failover-timeout mymaster 180000 # start second sentinel src/redis-sentinel sentinel_02.conf
At this point, we already have a master-slave setup with failover/failback capability. Now let’s do some tests.
# connect to first sentinel
src/redis-client -p 26379
# query sentinel for masters
127.0.0.1:26379> sentinel masters
# sample result (note the port of the master, 6379)
1) 1) "name"
2) "mymaster"
3) "ip"
4) "127.0.0.1"
5) "port"
6) "6379"
7) "runid"
8) "3c05872b72f10969855d580868ad883caf6e6a4b"
9) "flags"
10) "master"
11) "pending-commands"
12) "0"
13) "last-ok-ping-reply"
14) "260"
15) "last-ping-reply"
16) "260"
17) "info-refresh"
18) "5509"
19) "role-reported"
20) "master"
21) "role-reported-time"
22) "236203"
23) "config-epoch"
24) "0"
25) "num-slaves"
26) "1"
27) "num-other-sentinels"
28) "1"
29) "quorum"
30) "2"
31) "down-after-milliseconds"
32) "30000"
33) "failover-timeout"
34) "180000"
35) "parallel-syncs"
36) "1"
# query sentinel for attached slaves
127.0.0.1:26379> sentinel slaves mymaster
# sample result (note the port of the slave, 6380)
1) 1) "name"
2) "127.0.0.1:6380"
3) "ip"
4) "127.0.0.1"
5) "port"
6) "6380"
7) "runid"
8) "3a929c0e4f84a92e4998691699449ba0c23a641a"
9) "flags"
10) "slave"
11) "pending-commands"
12) "0"
13) "last-ok-ping-reply"
14) "958"
15) "last-ping-reply"
16) "958"
17) "info-refresh"
18) "4496"
19) "role-reported"
20) "slave"
21) "role-reported-time"
22) "325864"
23) "master-link-down-time"
24) "0"
25) "master-link-status"
26) "ok"
27) "master-host"
28) "127.0.0.1"
29) "master-port"
30) "6379"
31) "slave-priority"
32) "100"
33) "slave-repl-offset"
34) "41492"
# force a failover
127.0.0.1:26379> sentinel failover mymaster
# sample result
OK
# query sentinel for masters after failover
127.0.0.1:26379> sentinel masters
# sample result (note the new port, 6380 - slave has been promoted)
1) 1) "name"
2) "mymaster"
3) "ip"
4) "127.0.0.1"
5) "port"
6) "6380"
7) "runid"
8) "3a929c0e4f84a92e4998691699449ba0c23a641a"
9) "flags"
10) "master"
11) "pending-commands"
12) "0"
13) "last-ok-ping-reply"
14) "591"
15) "last-ping-reply"
16) "591"
17) "info-refresh"
18) "5628"
19) "role-reported"
20) "master"
21) "role-reported-time"
22) "13084"
23) "config-epoch"
24) "1"
25) "num-slaves"
26) "1"
27) "num-other-sentinels"
28) "1"
29) "quorum"
30) "2"
31) "down-after-milliseconds"
32) "30000"
33) "failover-timeout"
34) "180000"
35) "parallel-syncs"
36) "1"
# query sentinel for slaves after failover
127.0.0.1:26379> sentinel slaves mymaster
# sample result (note port of new slave, 6379 - original master is now slave)
1) 1) "name"
2) "127.0.0.1:6379"
3) "ip"
4) "127.0.0.1"
5) "port"
6) "6379"
7) "runid"
8) "3c05872b72f10969855d580868ad883caf6e6a4b"
9) "flags"
10) "slave"
11) "pending-commands"
12) "0"
13) "last-ok-ping-reply"
14) "565"
15) "last-ping-reply"
16) "565"
17) "info-refresh"
18) "4356"
19) "role-reported"
20) "slave"
21) "role-reported-time"
22) "14366"
23) "master-link-down-time"
24) "0"
25) "master-link-status"
26) "ok"
27) "master-host"
28) "127.0.0.1"
29) "master-port"
30) "6380"
31) "slave-priority"
32) "100"
33) "slave-repl-offset"
34) "59800"
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